The present invention relates to signal processing systems for eliminating pseudo-peaks in a waveform read from a recording medium in a digital magnetic writing and reading apparatus which uses a thin film head (hereinafter referred to as a TFH), a magneto-resistive head (hereinafter referred to as a MR head) or a metal-in-gap head (hereinafter referred to as MIG head).
In order to obtain a rapid writing magnetic field due to an increased recording density, a TFH has been used in a digital magnetic writing and reading apparatus using peak detection. Since a small-sized magnetic disk device is slow in line speed, a method of separation of a write head from a read head has been used in which a TFH writes data while an MR head reads data. In a small-sized designed for cost reduction, an MIG head is used. However, the use of the TFH generates a pseudo peak, or undershoot, that is reversed in polarity to a main peak of a read waveform in the vicinity of the outside pole-tip corner of a pole because of a limited pole-tip length. In the MIG head, a pseudo-peak of the same polarity as the main peak in a read waveform appears in the interface between a bulk portion and a metal film in the gap. In the MR head, a magnetic material called a shield is disposed on each side of the magneto-resistive film in order to improve its read resolution. The use of the shield causes the head itself to slim the read waveform as well as to cause a pseudo-peak to occur simultaneously. When pattern data are read under such conditions, the pseudo-peak causes intersymbol interference with the read waveform in the vicinity thereof, so that a pattern peak shift would increase.
Thus, conventionally, undershoots in the TFH have been eliminated using a transversal equalizer as disclosed in JP-A-60-136902 (U.S. Pat. No. 4,644,424) and JP-A-61-59664 and a multi-tapped equalizer including a reflection path as disclosed in JP-A-61-99906, 61-114611 and 61-139980. In these methods, an echo signal whose waveform deviates timewise from its input signal is produced by a signal delay circuit and added to the input signal at a ratio to thereby compensate for the undershoot.